"Occasionally a line of gray cars crawls along an invisible track, gives out a ghastly creak, and comes to rest..."

"... and immediately the ash-gray men swarm up with leaden spades and stir up an impenetrable cloud, which screens their obscure operations from your sight."

Yesterday, I told you I'd heard myself mutter "ah, there's a great gatsby sentence," and I'd wondered if I'd said "a 'Great Gatsby' sentence" or "a great 'Gatsby' sentence." I told you it was a doozy... a daisy. And now, it's today, and that's the sentence. Isn't it quite something?

A spooky gray, ghastly, ash-gray, swarming, leaden, impenetrable, obscure thing happens. We see... that we can't see it. It's invisible, out of sight, obscure,  screened, clouded, and impenetrable. So much about unseen sights and the one — only one — sound, a ghastly creak. What's going on? It's an operation, done with shovels. An obscure operation.

Occasionally an Obscure Operation. You can use that for the title of your next novel.